1. U.S. Pat. 4,661,639 to Asahi chem. Co. (1985).
2. O. Mitsuie Y. Fukuoka, U.S. Pat. 4,678,861 to Asahi chem. Co. (1987).
3. W.L. Drinkart, NL Pat. 7,205,832 to Dupont de Nemours, 1972.
4. M.M. Johnson, G.P. Nowack, U.S. Pat. 3,793,383 to Philips Petroleum, 1974.
5. H. Ichicashi, Eur. Pat. 214530 to Sumitomo Chem. Co. (1987).